Method For Producing Catalysts Having Increased Strength And Decreased Volume Reduction

ABSTRACT

A method for producing catalysts containing copper, in particular for producing catalyst moldings having increased mechanical strength and low volume reduction, to the catalysts produced by means of the method according to the invention, and to the use of said catalysts as catalysts or as precursors and components for catalysts. The catalysts are suitable in particular for the synthesis of methanol and for the low-temperature conversion of CO into CO2.

The invention relates to a process for producing copper-containingcatalysts, in particular shaped catalyst bodies having increasedmechanical strength and a low volume shrinkage, and also the shapedcatalyst bodies produced by the process of the invention and the usethereof as catalysts or as precursors and components for catalysts. Thecatalysts of the invention are particularly suitable for the synthesisof methanol and for the low-temperature conversion of CO into CO₂.

BACKGROUND OF THE INVENTION

Copper-containing catalysts are used on a large scale in the productionof basic and fine chemicals, e.g. in the catalytic conversion ofmixtures of CO₂, CO and H₂ into methanol. The properties of suchcatalysts can be varied as a function of various parameters, e.g. by thechoice of support material or via the size and shape of the metalparticles. The activity of these catalysts having copper as activecomponent is generally dependent on the size of the metal particles.

Copper-containing catalysts are often produced by means of a multistageprocess. Here, a catalyst precursor material is produced in a first stepfrom the copper component and also further components which have astabilizing support function on the active component in the futurecatalyst. This is usually effected by coprecipitation of all desiredcomponents. After washing to remove excess salts or undesirable (alkali)metals, drying is carried out to give a solid catalyst precursormaterial. In a further step, this solid catalyst precursor is treatedthermally and converted into a largely oxidic state. This is followed byshaping of the catalyst composition by tableting, granulation, extrusionor by a combination of the methods mentioned. Finally, the shaped bodyobtained is converted by means of hydrogen, carbon monoxide orwet-chemical reducing agents into the catalytically active, finelydivided copper metal.

Methanol synthesis plants are usually charged with the oxidic catalystin pellet form and this is subsequently converted in-situ into thecatalytically active catalyst by means of reduction in a stream ofhydrogen according to appropriate activation processes.

For example, DE 10 2005 020 630-A1, WO 03/053569, DE 3317 725 A1 and DE101 60 487 A1 describe the production of copper-based catalysts for thesynthesis of methanol.

However, the catalysts produced in the manner described have thedisadvantage that they suffer from pronounced volume shrinkage as aresult of reduction, which is also associated with a significantdecrease in the mechanical strength of the shaped body. There are manyreasons for the pronounced volume shrinkage of copper-containing shapedcatalyst bodies during reduction. For example, the shaped body canshrink due to the volume contraction during transformation from theoxidic state into the metallic state. Further reasons are thecondensation of water vapor which is usually formed in the reduction,which can lead to collapse of the pore structure of the shaped catalystbody. However, a very low volume shrinkage of the shaped body isdesirable for optimal utilization of the catalyst bed in the reactorduring operation. An increased volume shrinkage of the catalyst bed inthe reactor leads to poorer utilization of the reactor (part of thereactor remains empty) and poorer utilization of the heat transfer areaof the reactor. The latter is particularly problematical since coolingof the catalyst bed usually represents a limiting factor duringoperation.

In principle, the reduction step can also be carried out before loadingof the reactor with the catalyst by reduction and subsequent passivationunder mild conditions by means of an oxidant, generally by means ofgaseous oxygen (reduction stabilization) or by wet-chemicalstabilization by means of an oil. However, the copper catalysts producedin this way usually have the disadvantages that (i) a further processstep associated with additional costs is necessary in production of thecatalyst, that (ii) the copper catalyst has a significantly lowermechanical strength compared to the unreduced (oxidic) state, whichshows up, in particular, by increased fracture in the catalyst bedcompared to the oxidic state during loading of the reactor, and that(iii) the reduction-stabilized catalysts are not storage-stable andreoxidize by contact with air over time. Here, reference may be made,for example, to the document EP 1 238 702 A1.

A high mechanical strength is demanded of shaped bodies, e.g. pellets,so that they can survive the stresses which act on them at the time ofcharging of the reactor and also during operation without sufferingdamage. However, the reduction of catalysts is generally also associatedwith a significant reduction in the mechanical strength. Particularly inthe case of reduced metal catalysts in the form of pellets, the lateralcompressive strength, as a measure of the mechanical strength ofpellets, is many times lower compared to the lateral compressivestrength in the oxidic state. Correspondingly, the mechanical strengthof the pellets is also many times lower after reduction than in theoxidic state. As a result of vibrations, external and internal pressurefluctuations in the reactor during operation and/or the weight of thecatalyst bed on the individual shaped catalyst bodies, the pellets arehighly stressed during operation by rubbing against the reactor wall orby rubbing of the pellets against one another, which in particular as aresult of the stresses arising at the edges and corners of the pelletsleads to increased abrasion of the pellets.

It is therefore an object of the present invention to provide aproduction process by means of which copper-containing shaped catalystbodies having greatly reduced, preferably absolutely no, volumeshrinkage after activation (reduction to the metal) combined with highmechanical strength can be obtained. The process should also be simpleto carry out and inexpensive. The catalysts obtained should preferablybe able to be used for the synthesis of methanol.

SUMMARY OF THE INVENTION

The invention provides a process for producing a shaped catalyst bodycontaining copper, zinc and aluminum, which comprises the followingsteps:

-   (a) combining of an alkaline solution, in particular a    carbonate-containing precipitate,    -   with a copper-containing solution, which is obtainable by        dissolving and/or suspending a copper compound, a zinc compound        and an aluminum compound,    -   to give a precipitate;-   (b) isolation, optionally washing and/or optionally drying of the    precipitate to give a solid catalyst precursor;-   (c) thermal treatment at a temperature in the range from 200° C. to    600° C. of the solid catalyst precursor obtained in step (b) to give    a mixed oxide, preferably a mixed oxide having a BET surface area in    the range from 80 m²/g to 140 m²/g, more preferably in the range    from 85 m²/g to 120 m²/g, particularly preferably in the range from    90 m²/g to 110 m²/g;-   (d) mixing of solid catalyst precursor obtained in step (b) with    mixed oxide obtained in step (c) in a weight ratio of solid catalyst    precursor to mixed oxide in the range from 2:98 to 20:80, preferably    in the range from 5:95 to 15:85, more preferably in the range from    10:90 to 15:85, to give a mixture; and-   (e) tableting of the mixture obtained in step (d).

In addition, the invention provides shaped catalyst bodies which can beproduced by the process of the invention.

The invention also provides for the use of shaped catalyst bodiesproduced by the process of the invention for the synthesis of methanolfrom synthesis gas containing CO₂, CO and H₂ or for the low-temperatureconversion of CO into CO₂.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention for producing a shaped catalyst bodycomprises combining of a copper-containing solution with an alkalinesolution to form a precipitate in step (a).

The copper-containing solution is produced by dissolving and/orsuspending a copper compound, a zinc compound and an aluminum compoundin a suitable solvent in a vessel. As an alternative, a copper compound,a zinc compound and an aluminum compound can be dissolved and/orsuspended in a plurality of vessels and the resulting solutions can becombined to give the copper-containing solution.

For the purposes of the present invention, the formulation “solution”includes both solutions and also suspensions and slurries, withsolutions and suspensions being preferred.

The solvent for producing the copper-containing solution (or forproducing the individual solutions which are combined to produce thecopper-containing solution) is preferably water or an aqueous acid suchas aqueous hydrochloric acid (HCl), aqueous nitric acid (HNO₃), aqueoussulfuric acid or mixtures thereof, in particular water or aqueous nitricacid.

The copper-containing aqueous solution preferably has a pH in the rangefrom 0 to 7, more preferably in the range from 1 to 5, particularlypreferably in the range from 2 to 4.

As copper compounds, it is in principle possible to use both copper inmetallic form and preferably all compounds of copper which are readilysoluble in water, acids or alkalis, in particular the compounds ofcopper which are readily soluble in water and/or acids, in particularthe salts of copper, very particularly the nitrates; sulfates; halidessuch as chlorides, bromides and/or iodides; carbonates; oxides;hydroxides; hydrogencarbonates and/or acetates of copper. The coppercompound is preferably copper nitrate. Particular preference is given tousing an aqueous, in particular acid, copper nitrate solution in theprocess of the invention.

As zinc compounds, it is in principle possible to use both copper inmetallic form and preferably all compounds of zinc which are readilysoluble in water, acids or alkalis, in particular the compounds of zincwhich are readily soluble in water and/or acids, in particular the saltsof zinc, very particularly the nitrates; sulfates; halides such aschlorides, bromides and/or iodides; carbonates; oxides; hydroxides;hydrogencarbonates and/or acetates of zinc. The zinc compound ispreferably zinc nitrate. Particular preference is given to using anaqueous, in particular acidic, zinc nitrate solution in the process ofthe invention.

As aluminum compounds, it is in principle possible to use both aluminumin metallic form and preferably all compounds of aluminum which arereadily soluble in water, acids or alkalis, in particular the salts ofaluminum, very particularly preferably the nitrates; sulfates; halidessuch as chlorides, bromides and/or iodides; oxides; hydroxides and/oracetates of aluminum. The aluminum compound is preferably aluminumnitrate.

Further preferred aluminum compounds include sodium aluminates andaluminum hydroxide sols and mixtures thereof.

As aluminum hydroxide sol, it is possible to use, for example, acommercially available product, e.g. a peptized boehmite or pseudoboehmite. In this case, a suspension comprising copper, zinc andaluminum compounds is formed by combining of the copper and zinccompounds with the aluminum hydroxide sol. As an alternative, thealuminum hydroxide sol can also be obtained by combining an aqueous,alkaline sodium aluminate solution (pH>9) with an acidic copper and zincsalt solution (pH<1). In this case, a preprecipitated, acidic suspension(pH 3.0) containing copper, zinc and aluminum compounds is formed bycombining of the copper, zinc and aluminum compounds.

The alkaline solution is, in particular, produced by dissolving alkalimetal compounds, alkaline earth metal compounds and/or ammoniumcompounds, in particular alkali metal and/or ammonium compounds,particularly preferably carbonates, hydrogencarbonates and/or hydroxidesthereof, in a suitable solvent, in particular water.

The alkali metal compounds, alkaline earth metal compounds and ammoniumcompounds are preferably selected from the group consisting of alkalimetal carbonates such as lithium, sodium, potassium, rubidium or cesiumcarbonate, alkali metal hydroxides such as lithium, sodium or potassiumhydroxide, alkaline earth metal carbonates such as magnesium, calcium,strontium or barium carbonate, ammonium carbonate, ammonium hydroxideand mixtures thereof. It is likewise possible to use the correspondinghydrogencarbonates or any mixtures of carbonates and hydrogencarbonatessimultaneously with or instead of the carbonates.

An aqueous alkali metal and/or ammonium carbonate solution, an aqueousalkali metal and/or ammonium hydrogencarbonate solution, an aqueousalkali metal and/or ammonium hydroxide solution, in particular anaqueous sodium carbonate solution, an aqueous sodium hydrogencarbonatesolution and/or an aqueous ammonium hydroxide solution (NH₃ in water),particularly preferably an aqueous sodium carbonate solution and/or anaqueous sodium hydrogencarbonate solution, is preferably used asalkaline solution.

The alkaline aqueous solution preferably has a basic pH in the rangefrom 7 to 14, more preferably in the range from 8 to 14, particularlypreferably in the range from 10 to 13.

Combining of the copper-containing solution (which contains copper, zincand aluminum) with the alkaline solution results in formation of aprecipitate.

In one embodiment, the combining can be carried out by introducing theabovementioned solutions simultaneously into a joint vessel, for examplea precipitation vessel. In this case, the two solutions are introduced,preferably continuously, into the reaction volume of a precipitationmixer. In a further embodiment, combining can also be effected byintroducing the one solution into the other solution which has beeninitially charged, for example in a vessel such as a precipitationvessel. In a preferred embodiment, combining of the solutions iseffected by introducing a volume stream of the copper-containingsolution into the appropriate alkaline solution which has been initiallyplaced in a precipitation vessel.

Before the combining, the copper-containing solution is preferablyheated to a temperature of 20° C. or more, for example to a temperaturein the range from 50° C. to 90° C., in particular to about 65° C., andpreferably stirred.

The alkaline solution is likewise preferably heated to a temperature of20° C. or more, for example to a temperature in the range from 50° C. to90° C., in particular to about 65° C., and stirred before the combining.

In a preferred embodiment, both the copper-containing solution and thealkaline solution are heated to a temperature in the range from 50° C.to 90° C., in particular to about 65° C., and stirred.

When solutions of the abovementioned solution pairs are combined, aprecipitate is formed in the mixture (hereinafter also referred to asprecipitate-containing solution mixture). Combining of the solutions isgenerally carried out in a stirred vessel. The vessel is preferablystirred by means of an inclined blade stirrer, propeller stirrer orother commercial stirrers.

The precipitate-containing solution mixture is preferably maintained ata temperature of 20° C. or more and in particular at a temperature inthe range from 50° C. to 90° C., preferably at about 65° C. In aparticularly preferred embodiment of the invention, theprecipitate-containing solution mixture is maintained at a temperaturein the range from 50° C. to 90° C., preferably at a temperature of about65° C., for at least 30 minutes, preferably from 1 hour to 36 hours, inparticular about hours, in order to complete the formation of theprecipitate if necessary or to increase the crystallinity of theprecipitate by aging.

Until precipitate formation is complete, the pH of theprecipitate-containing solution mixture is usually kept constant bymethods known to those skilled in the art. For example, the rate ofintroduction of solutions can be selected so that a particular pH isestablished in the precipitate-containing solution mixture. The pH ofthe precipitate-containing solution mixture is preferably in the rangefrom 5.0 to 8.5, in particular in the range from 6.0 to 7.5, preferablyabout 6.5.

The precipitate obtained in step (a) is preferably separated off byfiltration in step (b). As an alternative, the precipitate can beseparated off by decantation or centrifugation.

The isolated precipitate is optionally subjected to one or more washingsteps and subsequently optionally dried. Isolation, optionally washingand optionally drying of the precipitate gives a solid catalystprecursor.

The washing of the precipitate can, for example, be carried out byfirstly separating the precipitate-containing solution mixture from theprecipitate by use of a filter press and subsequently passing waterthrough the material in the filter press, thereby washing the material.As an alternative, the isolated precipitate can, after theprecipitate-containing solution mixture has been separated off byfiltration, decantation or centrifugation, be slurried in a vessel andsubsequently separated off from the liquid phase again by means of afilter press, a centrifuge or a decanter. This procedure is generallycarried out one or more times until a particular content of sodium ionsin the filter residue, i.e. in the filtercake, has been reached. Thecontent of sodium ions can be determined by atomic absorptionspectroscopy (AAS). The content of sodium in the filtercake after thelast washing operation is preferably 500 ppm or less, more preferablyless than 400 ppm or less, in particular 350 ppm or less. As analternative, washing can also be carried out until a particularconductivity of the filtrate has been reached. Here, the conductivitygenerally correlates with the concentration of sodium ions. Theconductivity of the filtrate from the last washing operation ispreferably 0.5 mS/cm or less, in particular 0.2 mS/cm or less. Theconductivity is determined in accordance with DIN 38404, part 8.

The isolated and optionally washed precipitate is then preferablysubjected to drying. Drying is carried out by heating the precipitate toa temperature in the range from 75° C. to 130° C., preferably in therange from 105° C. to 115° C.

In a particularly preferred embodiment, drying is carried out by spraydrying. For this purpose, a suspension having a solids content of 10 to40% by weight is produced from the isolated precipitate, e.g. afiltercake, by means of water. This suspension is then preferablyintroduced via a nozzle into a spray dryer. The temperature in the spraydryer during drying is preferably in the range from 75° C. to 130° C.,in particular in the range from 105° C. to 115° C. The outputtemperature characteristic for drying is preferably in the range from105° C. to 115° C. and is usually controlled via parameters such asamount of suspension sprayed in, the solids content of the suspension(and thus the amount of water which has to be evaporated) or temperaturein the spray dryer. The treatment of the material by means of the spraydryer results, in particular, in a dry powder.

Part of the solid catalyst precursor obtained in step (b) is subjectedto a thermal treatment in step (c), giving a mixed oxide.

In the thermal treatment, the metals are (at least partially) convertedinto the corresponding oxides by decomposition of the carbonates in theoptionally spray-dried precursor material. The specific BET surface areais in the range from 80 m²/g to 140 m²/g, preferably in the range from85 m²/g to 120 m²/g, particularly preferably in the range from 90 m²/gto 110 m²/g. This can be controlled via the temperature and duration ofthe thermal treatment (calcination). Preferred calcination temperaturesare in the range from 200° C. to 600° C., preferably in the range from270° C. to 550° C. and particularly preferably in the range from 450° C.to 500° C. The duration of the thermal treatment is preferably from 1hour to 5 hours, more preferably from 2.5 hours to 4 hours, particularlypreferably about 3 hours.

In a particularly preferred embodiment, the thermal treatment is carriedout for a period of from 2.5 hours to 4 hours at a temperature in therange from 450° C. to 500° C.

The thermal treatment can be carried out in air, in oxygen or underprotective gas such as argon or nitrogen or mixtures thereof. Thethermal treatment can be carried out batchwise, e.g. in a tray furnace,or continuously, e.g. in a rotary tube furnace.

In step (d), the mixed oxide obtained in step (c) is mixed with part ofthe solid catalyst precursor obtained in step (b) (which has not beensubjected to a thermal treatment). The weight ratio of solid (notthermally treated) catalyst precursor to thermally treated catalystprecursor (mixed oxide) is in the range from 2:98 to 20:80, preferablyin the range from 5:95 to 15:85, more preferably in the range from 10:90to 15:85.

The mixture obtained in step (d) is subsequently (preferably withaddition of lubricant) tableted in a step (e).

Tableting is preferably carried out by means of a tableting press, forexample a Korsch tableting press. Pellets having a diameter d of from 1mm to 10 mm, preferably from 1.5 mm to 8 mm and particularly preferablyfrom 4 mm to 6 mm, and a height h of from 1 mm to 10 mm, preferably from1.5 mm to 8 mm and particularly preferably from 3 mm to 4 mm, can beobtained by means of the tableting operation.

Tableting is preferably carried out with addition of a lubricant such asgraphite, oils or stearates, in particular graphite. The mixtureobtained (in step (d)) of thermally treated mixed oxide (from step (c))and solid catalyst precursor (from step (b)) is mixed with lubricants,in particular graphite, optionally compacted and/or granulated and thentableted in step (e). The lubricant is preferably added before tabletingin an amount in the range from 0.1 to 5% by weight, based on the totalweight of the composition to be tableted. The lubricant is morepreferably added in an amount in the range from 0.5 to 5% by weight,particularly preferably in an amount in the range from 1 to 3% byweight, preferably about 2% by weight, based on the total weight of thecomposition to be tableted.

The shaped catalyst body obtained after tableting preferably has alateral compressive strength based on the pellet weight, measured inaccordance with DIN EN 1094-5, in the range of 550 N/g or more,preferably in the range from 600 N/g to 1300 N/g, in particular in therange from 600 to 900 N/g.

In a preferred embodiment, the tableted shaped catalyst bodies have adiameter d in the range from 4 mm to 6 mm and a height h in the rangefrom 3 mm to 4 mm, and have a lateral compressive strength, based on thepellet weight, in the range from 600 to 900 N/g.

The tableted shaped catalyst bodies preferably have a loss on ignitionof 7.5% by weight or less, preferably 5.5% by weight or less, inparticular in the range from 0.1 to 4.0% by weight.

In a further preferred embodiment, the shaped catalyst body obtained hasa lateral compressive strength based on the pellet weight, measured inaccordance with DIN EN 1094-5, in the range from 600 to 900 N/g and aloss on ignition in the range from 0.1 to 4.0% by weight.

In a further embodiment, the tableted mixture obtained in step (e) isreduced in a further step (f).

Reduction is preferably effected by heating the tableted shaped catalystbody in a reducing atmosphere. In particular, the reducing atmosphere ishydrogen.

Reduction is, for example, carried out at a temperature in the rangefrom 150° C. to 450° C., in particular in the range from 180° C. to 300°C., preferably in the range from 190° C. to 290° C., particularlypreferably at about 250° C.

Reduction is, for example, carried out, depending on the amount ofcatalyst to be reduced, for a period of from 1 hour (for, for example,500 g) to 10 days (for, for example, 60 metric tons), in particular fora period of from 2 hours to 120 hours, preferably for a period of from24 to 48 hours. Amounts of catalyst corresponding to the productionscale (for example in the range from 1 to 60 metric tons) are preferablyreduced for a period of from 3 to 8 days. In a preferred embodiment,reduction is carried out at a temperature in the range from 190° C. to210° C.

After reduction, the shaped catalyst bodies are preferably stabilizedwet or dry. In the case of wet stabilization, the shaped bodies arecovered with liquid in order to avoid contact with oxygen as far aspossible. Suitable liquids include organic liquids and water, preferablyorganic liquids. Preferred organic liquids are those which at 20° C.have a vapor pressure of 0.5 hPa or less. Examples of suitable organicliquids are isodecanol, fatty alcohols such as Nafol® from Sasol,hexadecane, 2-ethylhexanol, propylene glycol and mixtures thereof, inparticular isodecanol.

In the case of dry stabilization, a mixture of oxygen or anoxygen-containing gas, preferably air, and an inert gas such as argon ornitrogen is introduced into the reduction reactor. The concentration ofoxygen in the mixture is preferably increased from about 0.04% by volumeto about 21% by volume. For example, a mixture of air and inert gas canbe introduced, with the ratio of air to inert gas initially being about0.2% by volume of air to 99.8% by volume of inert gas. The ratio of airto inert gas is then gradually increased (e.g. continuously or stepwise)until finally 100% by volume, for example, of air is introduced (whichcorresponds to an oxygen concentration of about 21% by volume). Withoutwishing to be tied to a theory, it is presumed that the introduction ofair or oxygen results in formation of a thin oxide layer having athickness of, for example, from 0.5 nm to 50 nm, preferably from 1 nm to20 nm, in particular from 1 nm to 10 nm, on the surface of the catalyst,which protects the catalyst against further oxidation. In drystabilization, the reactor temperature is preferably 100° C. or less,more preferably from 20° C. to 70° C. and particularly preferably from30° C. to 50° C. After the stabilization, the catalyst is transportableand can be transported to the user/plant operator.

The volume shrinkage of the pellets after reduction and passivation isdetermined by measuring the pellet dimensions (diameter and height) of arepresentative number of 20 pellets.

The shaped catalyst bodies produced by the process of the inventiondisplay, in a particular embodiment, a volume shrinkage due to reductionof 8% or less, preferably 6% or less, in particular 5% or less.

The Cu/Zn atomic ratio in the shaped catalyst body can vary within widelimits, but is preferably matched to that of conventional methanolsynthesis catalysts. The Cu/Zn atomic ratio in the shaped catalyst bodyis preferably from 15:85 to 85:15, particularly preferably from 60:40 to75:25. The Zn/Al atomic ratio is preferably from 60:40 to 80:20,particularly preferably from 70:30 to 80:20.

In one preferred embodiment the Cu/Zn atomic ratio is from 15:85 to85:15 and the Zn/Al atomic ratio is from 60:40 to 80:20. In oneparticularly preferred embodiment the Cu/Zn atomic ratio is from 60:40to 75:25 and the Zn/Al atomic ratio is from 70:30 to 80:20.

The copper-containing shaped catalyst body of the invention is suitablefor industrial use. The term “shaped catalyst body” can, for thepurposes of the present invention, be used interchangeably with the term“catalyst”, in particular when the function as such is under discussion.

The invention also provides for the use of the above-described catalystfor the synthesis of methanol from synthesis gas, i.e. from gascontaining CO₂, CO and H₂. The synthesis gas usually consists of from 5%by volume to 25% by volume of carbon monoxide, from 6% by volume to 12%by volume of carbon dioxide, from 10% by volume to 30% by volume ofinert gases, e.g. nitrogen and/or methane, with hydrogen as balance.

The methanol synthesis is usually carried out at a temperature in therange from 200° C. to 300° C., preferably in the range from 210° C. to280° C., at a pressure in the range from 40 bar to 150 bar, preferablyin the range from 60 bar to 100 bar, and a space velocity in the rangefrom 2000 to 22 000 h⁻¹. The space velocity is defined as the ratio ofthe volume flow of synthesis gas to the spatial volume of the catalyst,e.g. of a catalyst bed, based on the time unit of 1 hour.

The copper-containing catalyst of the invention is also suitable for theconversion of CO into CO₂, in particular the low-temperature conversionof CO into CO₂. The conversion of CO into CO₂ occurs according to thefollowing reaction equation:

CO+H₂O<=>H₂+CO₂

The low-temperature conversion is usually carried out at a temperaturein the range from 170° C. to 270° C., preferably in the range from 190°C. to 240° C. The low-temperature conversion is usually carried out at apressure in the range from 1 bar to 40 bar, preferably in the range from10 bar to 35 bar. In a preferred embodiment, the low-temperatureconversion is carried out at a temperature in the range from 170° C. to270° C. and a pressure in the range from 1 bar to 40 bar, in particularat a temperature in the range from 190° C. to 240° C. and a pressure inthe range from 10 bar to 35 bar.

Determination of Physical Parameters

The physical parameters indicated in the present invention are, unlessindicated otherwise, determined as described below:

Determination of the BET surface area: The BET surface area isdetermined by the nitrogen single-probe method in accordance with DIN66132 on the pulverulent catalyst and on pellets having a diameter of 6mm and a height of 4 mm.

Determination of the loss on ignition: The determination of the loss onignition is carried out starting from the powder. To determine the losson ignition of the pellets, these are milled beforehand to give powder.The sample to be determined is weighed out into a porcelain cruciblewhich has previously been ignited at 600° C. for 3 hours in a mufflefurnace. The sample weighed into the ignited and tared porcelaincrucible is subsequently thermally treated at 600° C. for 3 hours in amuffle furnace, transferred to a desiccator and cooled to roomtemperature. The cooled crucible is reweighed. The loss on ignition at600° C. is determined from the mass difference.

Determination of the lateral compressive strength: The lateralcompressive strength (LCS) of the shaped bodies/pellets is determined inaccordance with DIN EN 1094-5, 1995-09 edition, refractory results forinsulation purposes part 5: “Bestimmung der Kaltdruckfestigkeitgeformter Erzeugnisse”. The determination is carried out using acommercial instrument, for example model SCHLEUNIGER 6-D or ERWEKA TBH310 MD, in accordance with the instrument manufacturer's instructions.Typically, the pressures applied to the cylindrical wall of the pelletswhen rupture occurs is determined for a plurality of pellets (e.g. from10 to 100, preferably from 10 to 30, for example 20 pellets). Thearithmetic mean of the values obtained (in N) is formed. The lateralcompressive strength based on the pellet weight (in N/g) is given bynormalization of the arithmetic mean obtained for the lateralcompressive strength on the basis of the arithmetic mean pellet weight.

Determination of the pore volume of the pellets: The pore volume isdetermined by the mercury intrusion method in accordance with DIN 66133on pulverulent oxidic catalyst and on pellets.

Examples

The invention will be illustrated in more detail with the aid of thefollowing, nonlimiting examples. Even though these examples describespecific embodiments of the invention, they serve merely to illustratethe invention and should not be interpreted as limiting the invention inany way. As a person skilled in the art will know, numerousmodifications can be carried out on these without going outside thescope of protection of the invention as defined by the accompanyingclaims.

Production of the Catalysts

To produce the catalysts, a 14% strength by weight aqueous sodiumcarbonate solution was prepared and heated to 50° C. In a second vessel,820 g of copper nitrate, 120 g of zinc oxide and 260 g of aluminumnitrate were dissolved in 900 g of water and 270 g of 68% strength byweight HNO₃ at 50° C. The nitrate solution and the sodium carbonatesolution were brought together simultaneously at a temperature of 65° C.while keeping the pH of 6.5 constant (precipitation). The suspension wascontinuously pumped from the precipitation vessel into an aging vessel.After the precipitation was complete, the suspension was aged at 70° C.for at least 120 minutes. The color changed from light blue(commencement of aging) to green (end of aging). After aging, thesuspension was filtered and the filtercake was washed until the sodiumcontent of the filtercake, determined by atomic absorption spectroscopy,was less than 350 ppm. The filtercake was slurried by addition of waterto an oxide concentration of 10% by weight and dried in a spray dryer atan inlet temperature of from 275° C. to 270° C. and an outlettemperature of from 105° C. to 115° C. to give a solid catalystprecursor. The solid catalyst precursor obtained was used for productionof the shaped catalyst bodies described below.

For the analytical determination of the composition, part of the solidcatalyst precursor was calcined at 330° C. for 2 hours. The chemicalcomposition (in % by weight) was as follows: 64.0% of CuO, 27.8% of ZnO,8.2% of Al₂O₃. The solid catalyst precursor was subsequently thermallytreated at various temperatures (step (c)) and in the case of the shapedcatalyst bodies according to the invention mixed in the indicated ratiowith solid catalyst precursor material which had not been thermallytreated (step (d)). Finally, the mixture was tableted with addition ofin each case 2% by weight of graphite, based on the weight of themixture, to give pellets having a diameter of 6 mm and a height of 4 mm(step (e)).

Comparative catalyst 1 (Ex11519.01): The thermal treatment was carriedout at 400° C. in a muffle furnace for 3 hours. The powder obtained hada BET surface area of 119 m²/g and a loss on ignition of 11.9% byweight. 100 g of the powder were subsequently mixed with 2 g of graphiteand the mixture was tableted to give shaped bodies having a diameter of6 mm and a height of 4 mm. The lateral compressive strength based on thepellet weight was 1021.5 N/g.

Comparative catalyst 2 (Ex11519.02): The thermal treatment was carriedout at 430° C. in a muffle furnace for 3 hours. The powder obtained hada BET surface area of 117 m²/g and a loss on ignition of 9.0% by weight.100 g of the powder were subsequently mixed with 2 g of graphite and themixture was tableted to give shaped bodies having a diameter of 6 mm anda height of 4 mm.

The lateral compressive strength based on the pellet weight was 1020.4N/g.

Catalyst 1 (Ex11519.04): The thermal treatment was carried out at 460°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 114 m²/g and a loss on ignition of 4.4% by weight. 95 gof the powder were subsequently mixed with 5 g of material which had notbeen thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 868.2 N/g.

Catalyst 2 (Ex11519.05): The thermal treatment was carried out at 500°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 99 m²/g and a loss on ignition of <0.5% by weight. 95 gof the powder were subsequently mixed with 5 g of material which had notbeen thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 792.3 N/g.

Catalyst 3 (Ex11519.06): The thermal treatment was carried out at 500°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 99 m²/g and a loss on ignition of <0.5% by weight. 90 gof the powder were subsequently mixed with 10 g of material which hadnot been thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 894.7 N/g.

Catalyst 4 (Ex11519.07): The thermal treatment was carried out at 500°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 99 m²/g and a loss on ignition of <0.5% by weight. 85 gof the powder were subsequently mixed with 15 g of material which hadnot been thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 899.1 N/g.

Catalyst 5 (Ex11519.08): The thermal treatment was carried out at 550°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 92 m²/g and a loss on ignition of <0.5% by weight. 95 gof the powder were subsequently mixed with 5 g of material which had notbeen thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 570.1 N/g.

Catalyst 6 (Ex11519.09): The thermal treatment was carried out at 550°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 92 m²/g and a loss on ignition of <0.5% by weight. 90 gof the powder were subsequently mixed with 10 g of material which hadnot been thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give pellets having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 620.1 N/g.

Catalyst 7 (Ex11519.10): The thermal treatment was carried out at 550°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 92 m²/g and a loss on ignition of <0.5% by weight. 85 gof the powder were subsequently mixed with 15 g of material which hadnot been thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 618.4 N/g.

Catalyst 8 (Ex11519.11): The thermal treatment was carried out at 550°C. in a muffle furnace for 3 hours. The powder obtained had a BETsurface area of 92 m²/g and a loss on ignition of <0.5% by weight. 80 gof the powder were subsequently mixed with 20 g of material which hadnot been thermally treated (obtained from step (b)) and the mixture wastableted with addition of 2 g of graphite to give shaped bodies having adiameter of 6 mm and a height of 4 mm. The lateral compressive strengthbased on the pellet weight was 696.4 N/g.

TABLE 1 Physical properties of the oxidic catalysts obtained afterdirect tableting to give solid pellets having the dimensions d = 6 mmand h = 4 mm. BET LOI LCS LCS PV [m²/g] [% by wt.] [N] [N/g] [mm³/g]Comparative catalyst 1 92 14.0 244.5 1021.5 166.5 Comparative catalyst 297 8.9 248.7 1020.4 192.9 Catalyst 1 85 7.2 216.6  868.2 186.6 Catalyst2 84 4.6 194.8  792.3 202.8 Catalyst 3 83 5.4 218.1  894.7 208.5Catalyst 4 91 6.5 224.9  899.1 180.3 Catalyst 5 82 0.7 126.8  570.1289.6 Catalyst 6 83 1.1 142.7  620.1 222.9 Catalyst 7 87 1.9 140.2 618.4 221.4 Catalyst 8 90 2.3 156.1  696.4 241.3

Activation of the Catalysts

The catalysts of comparative catalysts 1 and 2 and the catalysts 1 to 4according to the invention obtained in pellet form were subsequentlyactivated, i.e. reduced in a stream of hydrogen. An amount of in eachcase 200 ml of the tested catalyst pellets was reduced withoutapplication of pressure, i.e. at atmospheric pressure (about 1.01325bar), in a reaction tube, with the pellets being heated according to atemperature program to 240° C. in flowing reduction gas (900l_(gas)/l_(catalyst)/h) consisting of 2% by volume of hydrogen and about98% by volume of nitrogen. The temperature was then increased to 250° C.and the reduction was completed in pure hydrogen (400l_(gas)/l_(catalyst)/h). The catalysts were cooled to room temperatureunder inert gas (nitrogen) and passivated on the surface in a dilutedoxygen atmosphere (0.5% by volume of oxygen and about 99.5% by volume ofnitrogen) at a maximum of 30° C.

The volume shrinkage of the pellets after reduction and passivation wasdetermined here by measuring the pellet dimensions (diameter and height)of a representative number of 20 pellets. Furthermore, the height of thecatalyst bed in the reduction reactor was measured before and afterreduction and the shrinkage of the catalyst bed was determined from thedifference. Both methods (determination of the pellet shrinkage anddetermination of the shrinkage of the catalyst bed) are equally suitablefor quantifying the shrinkage. Table 2 below shows the values for theaverage volume shrinkage of the pellets and for the average volumeshrinkage of the catalyst bed obtained for the six different shapedcatalyst bodies:

TABLE 2 Shrinkage of the catalysts obtained after reduction in a streamof hydrogen. Volume shrinkage Volume shrinkage of pellets [%] ofcatalyst bed [%] Comparative catalyst 1 −10.8 −11.2 Comparative catalyst2 −9.3 −8.2 Catalyst 1 −5.9 −5.3 Catalyst 2 −0.6 −2.4 Catalyst 3 −2.2−4.1 Catalyst 4 −1.9 −1.1

It can be seen from table 1 that the comparative catalysts in theunreduced state have a somewhat higher loss on ignition (and a somewhathigher BET surface area) compared to the catalysts according to theinvention. The lower loss on ignition of the shaped catalyst bodiesaccording to the invention correlates with a lower lateral compressivestrength based on the pellet weight.

However, the comparative catalysts display a significantly greatervolume shrinkage after reduction in a stream of hydrogen (see table 2).While shrinkages in the region of about 10% are observed in the case ofthe comparative catalysts, the shaped catalyst bodies according to theinvention display a significantly decreased shrinkage of from about 6%to less than 1%. The decreased shrinkage combined with a good mechanicalstrength allows improved utilization of the reactor volume and thus moreeconomical utilization of the shaped catalyst bodies.

In summary, it can thus be said that the shaped catalyst bodiesobtainable by the process of the invention are distinguished by a highmechanical strength combined with a greatly decreased shrinkage afterreduction.

1. A method for the synthesis reaction of methanol from synthesis gascontaining CO₂, CO and H₂ comprising the step of exposing the reactionto a shaped body catalyst obtained by the process comprising the stepsof: (a) combining an alkaline solution with a copper-containing solutionobtained by dissolving and/or suspending a copper compound, a zinccompound and an aluminum compound, to form a precipitate; (b) isolatingthe precipitate, with optional washing and/or optional drying thereof,to give a solid catalyst precursor; (c) thermally treating a first partof the solid catalyst precursor at a temperature in the range from 450°C. to 600° C. to provide a thermally-treated mixed oxide containingcopper, zinc and aluminum, while not thermally treating a second part ofthe solid catalyst precursor to provide a thermally-untreated solidcatalyst precursor containing copper, zinc and aluminum; (d) mixing thethermally-untreated solid catalyst precursor with the thermally-treatedmixed oxide in a weight ratio of solid catalyst precursor tothermally-treated mixed oxide in the range of 5:95 to 15:85, to give amixture; and (e) tableting the mixture of the thermally-untreated solidcatalyst precursor and the thermally-treated mixed oxide obtained instep (d), wherein a Cu/Zn atomic ratio of the shaped catalyst body isfrom 15:85 to 85:15 and a Zn/Al atomic ratio of the shaped catalyst bodyis from 60:40 to 80:20.
 2. A method for the conversion reaction of COinto CO₂ comprising the step of exposing the reaction to a shaped bodycatalyst obtained by the process comprising the steps of: (a) combiningan alkaline solution with a copper-containing solution obtained bydissolving and/or suspending a copper compound, a zinc compound and analuminum compound, to form a precipitate; (b) isolating the precipitate,with optional washing and/or optional drying thereof, to give a solidcatalyst precursor; (c) thermally treating a first part of the solidcatalyst precursor at a temperature in the range from 450° C. to 600° C.to provide a thermally-treated mixed oxide containing copper, zinc andaluminum, while not thermally treating a second part of the solidcatalyst precursor to provide a thermally-untreated solid catalystprecursor containing copper, zinc and aluminum; (d) mixing thethermally-untreated solid catalyst precursor with the thermally-treatedmixed oxide in a weight ratio of solid catalyst precursor tothermally-treated mixed oxide in the range of 5:95 to 15:85, to give amixture; and (e) tableting the mixture of the thermally-untreated solidcatalyst precursor and the thermally-treated mixed oxide obtained instep (d), wherein a Cu/Zn atomic ratio of the shaped catalyst body isfrom 15:85 to 85:15 and a Zn/Al atomic ratio of the shaped catalyst bodyis from 60:40 to 80:20.
 3. The method as claimed in claim 1, wherein thereaction occurs at a space velocity in the range from 2000 to 22 000h⁻¹, a pressure in the range from 60 to 100 bar and/or a temperature inthe range from 200° C. to 300° C.
 4. The method as claimed in claim 1,wherein the synthesis gas consists of from 5% by volume to 25% by volumeof carbon monoxide, from 6% by volume to 12% by volume of carbondioxide, from 10% by volume to 30% by volume of inert gases, withhydrogen as balance.
 5. The method as claimed in claim 2, wherein thereaction occurs at a pressure in the range from 1 to 40 bar and atemperature in the range from 170° C. to 270° C.
 6. The method asclaimed in claim 2, wherein the reaction occurs at a pressure in therange from 10 to 35 bar and a temperature in the range from 190° C. to240° C.
 7. The method as claimed in claim 1, wherein the shaped catalystbody has a lateral compressive strength based on the pellet weight of500 N/g or more.
 8. The method as claimed in claim 1, wherein the shapedcatalyst body has a loss on ignition of 7.5% by weight or less.
 9. Themethod as claimed in claim 1, wherein the copper-containing solution instep (a) comprises an aluminum hydroxide sol.
 10. The method as claimedin claim 1, wherein the copper-containing solution has a pH of 3.0. 11.The method as claimed in claim 1, wherein the shaped catalyst body has avolume shrinkage upon reduction of 6% or less.
 12. The method as claimedin claim 1, further comprising the step of: (f) reduction of thetableted mixture obtained in step (e).
 13. The method as claimed inclaim 12, wherein reduction is carried about by means of hydrogen. 14.The process as claimed in claim 1, wherein the Cu/Zn atomic ratio of theshaped catalyst body is from 60:40 to 75:25.
 15. The method as claimedin claim 1, wherein the Zn/Al atomic ratio of the shaped catalyst bodyis from 70:30 to 80:20.
 16. The method as claimed in claim 1, whereinthe thermally-untreated solid catalyst is mixed with the mixed oxide ina weight ratio of thermally-untreated solid catalyst precursor to mixedoxide in the range of 10:90 to 15:85.
 17. The process of claim 1,wherein the mixed oxide has a BET surface area in the range of 80 m²/gto 140 m²/g.
 18. The method as claimed in claim 1, wherein the Cu/Znatomic ratio of the shaped catalyst body is from 60:40 to 75:25 and theZn/Al atomic ratio of the shaped catalyst body is from 70:30 to 80:20.19. The method as claimed in claim 1, wherein the shaped catalyst bodyhas a lateral compressive strength based on the pellet weight of 500 N/gor more and a loss on ignition of 7.5% by weight or less.
 20. The methodas claimed in claim 1, wherein the shaped catalyst body has a lateralcompressive strength based on the pellet weight of 500 N/g or more and avolume shrinkage upon reduction of 6% or less.